Signal control circuits



y 0, 1938. a. G. BJCRNSON 2,116,558

SIGNAL CONTROL CIRCUITS Filed May 11, 1935 2 Sheets-Sheet l arm INVENTORB. G. BJORNSON ATTORNEY May 10, 1938. g b so 2,116,558

SIGNAL CONTROL CIRCUITS I Filed May 11, 1935 2 Sheets-Sheet 2 ix v iig:k

l/vvsA/rok 5.0. woRA/so/v' A TTORA/EV Patented May 10, 1938 UNITEDSTATES PATET QFFEE SIGNAL CONTROL CIRCUITS Application May 11, 1935,Serial No. 20,965

16 Claims.

This invention relates to control circuits and particularly to controlcircuits for adjusting the net loss on signal transmission lines.

One object of the invention is to provide a signal transmission linewith control circuits that shall transmit over the line an impulse ofcontrol current having a frequency within the signal frequency range andcontrolled by the signal currents for governing the net loss on thetransmission line.

Another object of the invention is to provide a signal transmission linewith control circuits that shall transmit over the line between currentsrepresenting words of speech an impulse of control current having afrequency Within the voice frequency range and under control of thespeech currents for adjusting the net loss on the transmission line.

Another object of the invention is to provide a signal transmission linewith control circuits governed by the amplitude of speech currents thatshall transmit over the line between currents representing words ofspeech an impulse of control current having a frequency within the voicefrequency range for adjusting the net loss on the line at a distantstation thereon.

A further object of the invention is to provide a signal transmissionline with control circuits governed by the amplitude of speech currentsat a transmitting station that shall transmit over the line betweencurrents representing words of speech an impulse of control currenthaving a frequency Within the voice frequency range and with controlcircuits at a receiving station that shall govern the net loss on theline at the receiving station according to the strength of the receivedimpulse of control current.

In a transmission line, it is necessary to provide repeater stations atintervals along the line and to control the gain at the repeaterstations for efiicient transmission of signal currents. When thetransmission line has considerable length, the small errors in theoperation of the regulators at the repeater station may add together andproduce an appreciable error at the In one form of the invention, asource of control current, which preferably has a frequency of the orderof 800 cycles, is connected to one side of a four-wire line to transmitan impulse of control current under control of the voice frequencycurrents. The source of control current may be connected to the line atpredetermined intervals under control of a timing circuit when there areno speech. currents on either the transmitting channel or the receivingchannel. A speech disabler circuit is provided for preventing solecontrol of the source of control current by the timing circuit whenthere are speech currents on either the transmitting channel or thereceiving channel. A speech control circuit and the timing circuitjointly govern the source of control current when speech currents are onthe channel to which the speech control circuit is connected.

At a receiving station, a starting circuit is operated when pure controlcurrent free from speech currents is received. The starting circuit,when operated, performs two functions. A gain control device in thetransmission line is governed to adjust the net loss on the line and afilter is inserted in the line beyond the gain control device forpreventing transmission of the control current to any of the speechreceiving apparatus.

The preferred speech control circuit comprises a relay which isconnected to the transmitting channels, by means of a space dischargedetector tube, a transformer, and an amplifier device. When speechcurrents for a loud syllable are transmitted over the transmission line,the relay is operated to increase the sensitivity of the detector outputcircuit a definite amount. This increase in the sensivity of thedetector output circuit operates a second relay which, in turn,cornpletes a circuit for charging a condenser. When the input level tothe detector tube falls below the initial operating level for the firstrelay, the second relay releases and the charge on the condensermomentarily operates a third relay. The third relay cooperates with thetiming circuit for connecting the source of control current to thetransmission line. The connection of the source of control current tothe line will, in most cases, take place during the pause between Wordsof speech. The chances are that this transmission of the control currenttakes place after the final consonant of a word has started, or if thesyllable ends with a vowel, that little harm will be done if the finalpart of the vowel is eliminated.

At the receiving end of the line, a starting circuit is providedcomprising a space discharge amplifier having an anti-resonant circuitand a resonant circuit connected to the output circuit thereof. Theresonant and anti-resonant circuits are tuned to the frequency of thecontrol current. The primary winding of a transformer is connected inshunt to the anti-resonant circuit and the primary winding of a secondtransformer is connected in shunt to the resonant circuit. Each of thesecondary windings of the two transformers is connected in circuit witha rectifying device to a coil of a starting relay. The coil connected tothe transformer whose primary is in shunt to the resonant circuit serveswhen supplied with rectified current in the right direction to produce aforce tending to hold the armature of the starting relay in releasedposition. The coil which is controlled by the anti-resonant circuitproduces a force when supplied with rectified current in the rightdirection to effect operation of the relay. If an impulse of purecontrol current free from any speech frequency currents is received bythe starting circuit, the starting relay will be operated. If currentsof other frequencies than the control current frequency are received bythe starting circuit, the coil connected to the resonant circuit willprevent operation of the starting relay.

A space discharge device is connected in the line at the receivingstation for governing the net loss on the line at the receiving station.The starting relay, when operated, completes a circuit for permitting abackward acting circuit to control the space discharge device in theline. The starting relay also serves, when operated, to insert a filterin the line beyond the gain control device. The filter is tuned to thefrequency of the control current. This filter serves to prevent any ofthe control current from reaching the receiving apparatus beyond thegain control device.

In the accompanying drawings- Fig. l is a diagrammatic view of a speechcontrol circuit governed according to the amplitude of the voicecurrents;

Fig. 2 of the drawings is a diagrammatic view of a modified speechcontrol circuit governed by the currents representing the vowel soundsof speech;

Fig. 3 of the drawings is a diagrammatic view of a modified speechcontrol circuit governed according to the frequencies of the currentsrepresenting the syllables of speech; and

Fig. 4 of the drawings is a diagrammatic view of the control circuits attransmitting and receiving stations on a transmission line for adjustingthe net loss on the line according to the invention.

Referring to Fig. 1 of the drawings, a speech control circuit is shownfor governing the connection of a control current to a transmission lineunder control of the voice currents. The control circuit comprises adetector tube i which is connected to a transmission line by means of atransformer 2. In the output circuit of the detector tube I are includedthe energizing coils of relays 3 and 4. The relay 3 is more sensitivethan the relay 4 and will be operated by the speech currentsrepresenting a loud syllable. Normally, when the relay 3 is in releasedposition, the armature of the relay engages a tap 5 extending from thesecondary winding of the transformer 2. When the relay 3 is operated,the armature engages the terminal of the secondary winding of. thetransformer 2 so that the complete secondary winding is connected to theinput circuit of the detector tube I. The operation of the relay 3serves to increase the sensitivity of the detector l a definite amount,for example, twenty decibels, and permits the operation of the relay 4.The relay a, which is less sensitive than the relay 3, releases when theinput level to the control circuit falls approximately twenty decibelsbelow the initial operating level of relay 3. The armature 6 of therelay 4 completes a circuit from a battery l for charging a condenser 3when the relay 4 is in operative position. Upon release of the relay 4,the charge on the condenser 8 serves to momentarily operate a relay 9.

Referring to Fig. 4 of the drawings, a fourwire transmission circuit,comprising transmitting conductors l and H and receiving conductors l2and i3, is provided with a transmitting station !4 governed by a speechcontrol circuit I of the type shown in Fig. 1 of the drawings. A sourceof control current it having a frequency preferably of the order of 800cycles is connected under control of a relay ll through a spacedischarge amplifier l8 to the transmitting conductors ill and I l. Therelay I1 is governed by a timing circuit [9 when speech currents are ofithe conductors i0 and H and i2 and I3 and is jointly controlled by thespeech control circuit l5 and the timing circuit [9 when speech currentsare on the conductors i0 and H.

The speech control circuit I5 shown in Fig. 4 of the drawings is thesame as the speech control circuit shown in Fig. 1 of the drawings andlike parts have been indicated by similar reference characters. Theprimary winding of the transformer 2 is shown connected to thetransmitting conductors i0 and H by means of an amplifier device 20.Batteries 2! and 22 are respectively provided for supplying potential tothe grid and the plate of the detector tube I. When speech currentsrepresenting a loud syllable appear on the conductors ID and II, therelay 3 will be operated. Relay 5, upon operation, increases thesensitivity of the detector tube 1 to effect operation of the relay 4.The relay 4 upon operation completes a circuit for charging thecondenser 8 from the battery 'I. When the input level of the detectortube l falls below the initial operating level for the relay 3, therelay 4 is released and the charge on the condenser 13 effects operationof the relay 9. In this circuit, it is assumed that the sensitivity ofthe speech control is so low that only the loud syllables, say onesyllable out of every one hundred syllables, will operate the relay 9.

The timing circuit l9 comprises a contact arm 23 which is rotated atconstant speed in any suitable manner. The arm 23 engages a conductingsegment 24 for one-fourth the rotation of the arm 23. The engagement bythe contact arm 23 and the contact segment 24 partially completes acircuit for operating a holding relay 25 from a battery 26. A speechdisabling circuit 21, which is connected to a hybrid coil 28, servesto-prevent operation of the relay 25 solely by the timing circuit when.speech currents are on the conductors l8 and H or l2 and L3. The hybridcoil 28 is connected to the conductors it and H by the amplifier device20 and to the conductors l2 and it by the amplifier device 29.

The speech disabler circuit 2'! comprises a gasfilled space dischargedevice 30 having the input circuit thereof connected to the hybrid coil28 by means of a transformer 3|. The output circuit of the gas-filleddevice 30 is connected to the operating coil of a relay 32. .A'condenser33 and a resistance 34 are connected to the output circuit of the device.39 for effecting a hangover in the operation of the relay 32 when thegasfilled device 39 is broken down. When speech currents appear on theconductors I9 and. II or I2 and I3, the gas-filled space dischargedevice 39 is broken down to effect operation of the relay 32 and toprovide a discharge path for the condenser 33. When speech currentscease to flow on the transmitting line or the receiving line, thegas-filled device 39 is extinguished. The condenser 33 is then chargedby a battery 35 through a circuit including the coil of the relay 32.The time taken to charge. the condenser 33 provides a hangover in theoperation of the relay 32.

If no speech currents are on the transmitting or receiving lines, therelay 32 is released and a ground circuit is provided for operating therelay 25 whenever the contact arm 23 engages the contact segment 24. Therelay I! is operated for each operation of the relay 25 by means of thecharge on a condenser 36. Relay I'I upon operation removes a shortacross the source of control current I6 so that an impulse of controlcurrent is transmitted through'the amplifier I8 to the conductors I9 andII.

If speech currents are on the conductors I9 and II, the relay 32 isoperated to prevent sole control of the source of control current I6 bymeans of the timing circuit I9. Under this circumstance, the speechcontrol circuit I5 must be operated with the timing circuit I9 to effectoperation of the relay I'I to connect the source of control current I6to the transmitting conductors I9 and II. The speech control circuit I5is operated as before set forth when speech currents for a loud syllableappear on the conductors I9 and I. The relay 25 is operated when thecontact arm 23 engages the contact segment 24 and the relays 9 and 32are in operative positions.

At the receiving end of the circuit, a space discharge device 49 isincluded in the transmitting line comprising conductors I9 and II. Atransformer 4| is connected to the input circuit of the device 49 and atransformer 42 is connected to the output circuit of the device 49. Adelay circuit 43 is connected to the secondary winding of thetransformer 42. A space discharge amplifier 44 is connected to the delaycircuit 43 and two transformers 45 and 46 are connected to thetransmitting line beyond the amplifier device 44. A filter 4'I, which istuned to the frequency of the control current, is connected to thetransmitting line between the transformers 45 and 46 under control of astarting relay 48 in a starting circuit 49.

The starting circuit 49 comprises a space discharge amplifier tube 59having the input circuit thereof connected to the conductors I9 and IIbefore the transformer 4| by means of a transformer 5|. A resonantcircuit 52 and an antiresonant circuit 53 are included in the outputcircuit of the amplifier tube 59. The resonant circuit comprises aninductance element 54 and a condenser 55. The anti-resonant circuitcomprises an inductance element 56 and a condenser 51. The anti-resonantcircuit 53 is shunted by the primary winding of a transformer 58. Theresonant circuit 52 is shunted by the primary winding of a transformer59. The secondary winding of the transformer 58 is connected to a coilof the starting relay 48 through a rectifier 69 of any suitable type.The secondary winding of the transformer 59 is connected to another coilof the starting relay 48 through a rectifier 6| of any suitable type.When the relay 48 is in released position, as shown in Fig. 4 of thedrawings, the filter 41 is short-circuited. When the relay 48 is inoperative position, the filter 41 is inserted in the transmittingchannel to prevent transmission of any control current beyond thetransformer 46 to the receiving apparatus thereafter. An impulse of purecontrol current free from currents of other frequencies effectsoperation of the coil of relay 48 connected to the transformer 58. Ifcurrents of other frequencies besides the 800 cycle control current arereceived by the starting circuit 49, the coil of the relay 48 connectedto the transformer 59 will be operated to insure against operation ofthe relay 48. I

The starting relay 48, when operated, not only effectively inserts thefilter 41 in the transmitting line but operates a relay 62. The relay62,

upon operation, connects a backward acting control circuit 63 to acontrol condenser 61 for governing the operation of the space dischargedevice 49. The backward acting control circuit 63 comprises a detectortube 64 having the input circuit thereof connected across the secondarywinding of the transformer 42 by means of a transformer 95. A resistanceelement 56, which is included in the. output circuit of the detectortube 64, is connected across the control concording to the strength ofthe impulse of control current. The delay circuit 43 serves to preventany transmission of the control current to any of the receivingapparatus beyond the transformer 46 prior to the operation of thestarting relay 49.

In the circuit above considered, it is preferable that a constant volumecontrol circuit of the type disclosed in the J. L. Hogg et a1. PatentNo. 1,853,974, dated April 12, 1932, is included in the system. It is tobe understood that other types of volume control may be employed. Ifsuch were not the case, a strong talker could operate the speech tonecircuit I5 on his weak syllable even though the number of line-ups wouldstill be definitely limited by the timing circuit I9.

Referring to Fig. 2, a modified speech control circuit I99 is shownwhich may be substituted for the speech control circuit I5 shown inFigs. 1 and 4 of the drawings. The speech control circuit shown in Fig.2 of the drawings comprises a detector tube I9I having the input circuitthereof connected to the secondary winding of the transformer 2 shown inFig. 4 of the drawings. The

output circuit of the detector tube IN is connected to a band-passfilter I02 which passes currents having frequencies of the order of to300 cycles. The band-pass filter I92 is connected by a transformer I93to the inputcircuit of a detector tube I94. The output circuit of thedetector tube I 94 includes the coil of a relay I95. The relay I95controls the relay 9 shown in Fig. 4

of the drawings by a circuit similar to the control 76 circuit for therelay 9 shown in Figs. 1 and 4 of the drawings.

The circuit shown in Fig. 2 of the drawings differentiates between thefrequencies'of-zthe cur rents representing vowels and consonants. Thevowels will have a prime frequency located within the band offrequencies passed by: the bandpassfilter I02. The band-pass filter N12is as sumed to pass only the pitch frequencies of the vowels. When thevowel sound is stopped, the relay 9 will operate. In this speech controlcircuit, the same as in the speech control circuit shown in Fig. l, theimpulse of control current will be applied during a silent period if theword causing the operation of the speech control circuit ends with avowel.

Themodified speech control circuit HG shown in Fig. 3 of the drawingsdoes not necessarily involve transmission of the control current at theend of a word although it could be so designed. The speech controlcircuit I H) comprises a relay HI having two coils H2 and H3. The relayHi serves the same purpose as the relay 9 shown in Figs. 1, 2, and 4 ofthe drawings. The coil H2 of the relay III which opposes. operation ofthe relay is controlled by a circuit extending from the secondary of thetransformer 2 through a band-pass filter H4, transformer H5, and adetector tube H 6. The band-pass filter H5 is assumed to passfrequencies of the order of 250 to '800 cycles. Coil H3 of the relay HIis controlled by a circuit extending through a pad I ll, a band-passfilter H8, a transformer H9, and a detector tube I20. The band-passfilter H8 passes currents having frequenciesbetween 800 and 2750 cycles.The relay H! will operate on loud syllables which have stronger energycomponents in the range of 800 to 2750 cycles per second rather than inthe frequency band included between 250 and 800 cycles per second. Thefrequency bands for the two filters H4 and H8 are tentative and optimumfrequency bands may be determined in accordance with transmittingconditions. The relative sensitivity of the two circuits, respectively,including the filters H4 and H8, can be varied by means of the pad H'l.

Modifications in the circuits and in the arrangement and location ofparts may be made within the spirit and scope of the invention and suchmodifications are intended'to be covered by the appended claims.

What is claimed is:

1. In combination, a two-wire signal transmission line, a transmittingstation, a source of control current at said station having a frequencywithin the voice frequency range, and means at said station undercontrol of the signal currents on said line for transmitting an impulseof said control current between transmission of currents representingcontiguous words in an uninterrupted transmission of speech.

2. In combination, a two-wire signal transmission line, a transmittingstation, a source of control current at said station having a frequencywithin the voice frequency range, a control circuit governed inaccordance with the'amplitude of the speech currents on said line, andmeans governed by said control circuit for transmitting an impulse ofsaid control current between transmission of currents representingcontiguous words in an uninterrupted transmission of speech.

3. In combination, a signal transmission line, a transmitting. station,a source of control current latsaid. station having a frequency Withinthe voice frequency range, a control circuit at said station governedin-accordance with the amplitude o-fthe signal currents on the line, atiming circuit at said station operated at predetermined time intervals,and: means jointly governed by said control circuit and the timingcircuit for transmitting an impulse of said control current betweentransmission of currents representing words in speech.

4. In combination, a signal transmission line, a transmitting station, asource of control current at said station having a frequency within thevoice frequency range, control means at said station operated whencurrents representing a loud syllable of speech are on the line andauxiliary means governed by said control means upon a'predeterminedreduction of the amplitude of the speech currents on the line fortransmitting an. impulse of said control current over the line.

5.2In combination, a'signal transmission line, a transmitting station, asource of control current at said station having a frequency within thevoice frequency range, a control circuit governed in accordance with theamplitude of the speech currents on the line, a timing circuit operatedat predetermined time intervals, an auxiliary circuit operated whenspeech currents are on said line, means jointly governed by said controlcircuit and the timing circuit for transmitting an impulse of saidcontrol current between transmission of currents representing words ofspeech when speech currents are being transmitted, and means jointlygoverned by said timing circuit and the auxiliary circuit fortransmitting an impulse of said control current at predetermined timeintervals when speech currents are not being transmitted over the line.

6. In combination, a. signal transmission line, a transmitting station,a source of control current at said station having a frequency withinthe voice frequency range, means comprising a relay operated whencurrents representing a loud syllable of speech are on the line, andmeans comprising a second relay operated upon release of said firstrelay after a predetermined reduction of the'amplitude of the speechcurrents on the line for transmitting an impulse of said controlcurrentover the line.

'7. In combination, a two-wire signal transmission line, a transmittingstation, a source of control current at said station having a frequencywithin the voice frequency range, and means controlled only by currentsrepresenting a vowel sound in speech on said line for effectingtransmission of an impulse of said control current over the line.

, 8. In combination, a signal transmission line, a transmitting station,a source of control current at said station having a frequency withinthe voice frequency range, and a control circuit having means forseparating the higher frequency speech currents from the lower frequencyspeech currents to control the transmission of an impulse ofsaid'control current over the line when the higher frequency componentsof the speech currents predominate.

9. In combination, a signal transmission line having signal currentstransmitted thereover,

means for transmitting impulses of control current over said line Withinthe frequency range of the signals transmitted over the line, areceiving station, a loss adjusting device in the line at said station,and means comprising a starting circuit operated only when a purecontrol current free from signal current is received for governing saiddevice to adjust the net loss on the line and for blocking the linebeyond said device to the transmission of the control current.

10. In combination, a signal transmission line having voice frequencysignal currents transmitted thereover, means for transmitting impulsesof control current over said line within the voice frequency range ofthe signals transmitted over the line, a receiving station, a spacedischarge device in the line at said station, a starting circuitoperated only when a pure control current free from signal currents isreceived, and means controlled by said starting circuit when operatedfor governing said device to adjust the net loss on the line and forblocking the line beyond said device to the transmission of the controlcurrent.

11. In combination, a signal transmission line having signal currentstransmitted thereover, means for transmitting impulses of controlcurrent over said line within the frequency range of the signalstransmitted over the line, a receiving station, a loss adjusting devicein the line at said station, delay means in the line beyond said device,a starting circuit operated only when a pure control current free fromsignal currents is received, means for blocking the line to the controlcurrent beyond said delay means, and means controlled by said startingcircuit when operated for governing said device to adjust the net losson the line and for operating said blocking means, said delay meansinsuring a delay in the transmission of the control current during theoperation of the starting circuit.

12. In combination, a signal transmission line having signal currentstransmitted thereover, a transmitting station, a source of controlcurrent at said station having a frequency within the frequency range ofthe transmitted signal currents, means at said station under control ofthe signals on the line from said station for transmitting an impulse ofsaid control current between signals representing words in anuninterrupted transmission of speech, a receiving station, and means atsaid receiving station responsive only to a transmitted impulse ofcontrol current free from signal currents for adjusting the net loss onthe line at the receiving station.

13. In combination, a signal transmission line having signal currentswithin the voice frequency range transmitted thereover, a transmittingstation, a source of control current at said station having a frequencywithin the voice frequency range of the transmitted signal currents,means at said station under control of the signal currents on the linefrom said station for transmitting an impulse of said control currentbetween transmission of currents representing contiguous words in anuninterrupted transmission of speech, a receiving station, a gaincontrol space discharge device in said line at the receiving station,and means at the receiving station responsive to a transmitted impulseof control current for governing said device to adjust the net loss onthe line at the receiving station and for blocking the line beyond saiddevice to the transmission of the control current when the controlcurrent is received.

14. In a transmission system, a method which consists in transmittingspeech signals over a transmission path, in transmitting currentimpulses over the path in the same direction as the speech signals andbetween contiguous words in an uninterrupted transmission of speech,.and in controlling the current impulses by the speech signals on thepath without interfering with the speech signals.

15. In combination, a two-wire signal transmission line, a transmittingstation, a source of control current, means at said station fortransmitting speech signals over said line, and means under control ofthe signals on said line for transmitting impulses of said controlcurrent over said line between contiguous words in an uninterruptedtransmission of speech without interference with the signals.

16. In combination, a two-wire signal transmission line, a transmittingstation, a source of control current at said station, means at saidstation for transmitting voice currents over said line, and means undercontrol of the voice currents for transmitting impulses of said controlcurrent over said line in the same direction as the voice currents andbetween contiguous words in an uninterrupted transmission of speechwithout interference with the voice currents.

BJ6RN G. BJ6RNsoN.

